THREE DIMENSIONAL ANATOMICAL STUDY OF CARPAL TUNNEL ( CADAVERIC STUDY )

The right wrist of twenty cadavers were examined to measure the three dimensions of the carpal tunnel by using a Vernia (INOX), the cross sectional area and volume were then calculated for males and females separately. All were above 40 years. Males were found to have larger carpal tunnel than females of the same age group, both in cross sectional area and volume. It was found also that the volume of the tunnel change according to the age. The pattern by which the volume changes is different in males and females. In active age group i.e. fourth to sixth decade, the tunnel volume in females’ collapse but it expand in males, this may explain the high incidence of carpal tunnel syndrome in females in this age group and the low number of affected males. The age / volume relation may shed some light on the etiology of the “Idiopathic” carpal tunnel syndrome.


Introduction
arpal tunnel syndrome (CTS) is the most frequently encountered peripheral neuropathy, specially in middle age women, it was first described in 1853 by Sir James Paget 1, since that time considerable researches were done to describe different clinical aspect of the syndrome as well as to identify the different etiological and causative factors.Local and systemic causes as well as various occupational hazards were to be blamed 2,3.In about half of the patients, a cause can be identified e.g.hypothyroidism, obesity, trauma to the hand, local tumor or ganglion, etc, but In the rest of the cases no abnormality or causative agents could be pointed 5,6 , these cases were classified as idiopathic carpal tunnel syndrome 3,7 .
In the last quarter of the 20 th century a trend begin to identify any anatomical abnormalities in size and volume of the carpal tunnel, this was facilitated by the new non-invasive techniques e.g.MRI, CT scan and Ultrasound.Many of these idiopathic cases were found to have anatomical abnormalities in the carpal bones i.e. stenosis of the carpal tunnel with the narrowing of the space available for the gliding of the nerve and tendons with their coverings as they pass through the tunnel from forearm to the hand.
The narrowing or stenosis of the tunnel may be minimum and the symptoms of median nerve compression arise only later in life when degenerative changes in the walls of the tunnel compete with the median nerve for space and it's function became impaired by compression of its arterial supply as ischaemic changes of its distal part may give rise to the feeling of numbness 6,8 .Symptoms may also become clinically apparent when other causes of compression is present e.g.pregnancy with retention of fluid 6 .The objective of this study is to determine the CSA of the proximal and distal ends and volume of the empty tunnel in males and females in vivo i.e. cadavers so as to determine the changes in CSA and volume as affected by age and sex and if these changes are of any significance, also if this volume changes is the sole cause of the syndrome, and the list of causes are only contributory factors.

Material and Methods
All the materials were obtained from the Department of Anatomy, College of Medicine and Department of Forensic Medicine, Basrah.
Examination of carpal tunnel (canal) of the right hand were done in 20 cadavers both fresh and formalin preserved, they were 10 females and 10 males.Their ages range from 44 -81 year.All the cadavers were presumed to have normal carpal tunnel as long as their families do not give any history of wrist diseases, and there was no scar of any previous operation.
The length, height and width of the proximal and distal ends of the carpal tunnel were measured after dividing the flexor retinaculum; using the vernia (INOX) to perform these measurements.
The length of the flexor retinaculum (transverse carpal ligament) was considered as equal to the length of the bonny tunnel.
The width of the tunnel, which is the transverse (long) diameter of the tunnel, was measured at proximal and distal ends.The inside distance between scaphoid and pisiform was recorded as the proximal width and the inside distance between triquitrum and hook of hammate as the width of the distal end.
The height (Depth) of the proximal and distal ends was obtained by measuring the depth between flexor retinaculum and the bottom of the carpal arch.
The cross section profile of both tunnel ends are not circular but rather elliptical then two diameters have to be measured i.e. width and height.In circular shape these two diameters are equal, but in elliptical shape an apparent intermediate axis have to be calculated 9 .The diameter of cross section profile were obtained by converting these elliptical profile measurements to those of circles using the equation: Were D is the new diameter of crosssection profile and L and S are the long and short axis measurements.
In this way circles of known diameter 10 could represent all cross section profile both circular and elliptical.
Then it is possible from D to measure the CSA as: CSA = (D / 2) 2 X π With the availability of the mean length for males and females, the volume for both sexes can be obtained as follows: Volume = mean CSA X length Were mean CSA = Proximal CSA / 2 + Distal CSA / 2. This volume represent the empty space through which the contents with their coverings are gliding, and it is the potential space for the expansion of the contents by e.g.synovitis or edema without exerting pressure on the median nerve.

Statistical analysis
Data were analyzed statistically using student " t" test of significance and "P" value.The tests of significance were done between males & females values.Females' samples were divided into below 40 years & above 40 years to match males' samples whom were all above 40 years.All the results were plotted into curves and tables.

Results
Age; in 10 males, the range of age was 44 -78 years, while in 10 females the age range from 20 -81 years.
The mean tunnel length was 28.4 ± 3.3 mm in males (Table I), and 26.2 ± 1.5 mm in females below 40 years (Table II), there is a difference in length of 2.2 mm between the sexes which is not significant (P>0.05).
The width of the tunnel was measured at proximal (inlet) and distal (outlet) ends (tables 1, 2 & 3).At the proximal end the mean width was 17.5 ± 2 mm in males and 16.9 ± 2.4 mm in females the difference is not significant (P>0.5).At the distal end, the measurement in males is 15.3 ± 2.2 mm and in females it is 14.7 ± 2.1 mm, again there is no significant difference between the two means (P>0.5).In comparing the width of proximal and distal area in both sexes, it was found that in males there is a difference of 2.2 mm which is significant (P<0.05).In females again the difference is 2.2 mm which is also significant (P<0.01).
The mean height in (Table I & II), proximal ends of the males is 10.7 ± 3.3 mm while in females it is 9.9 ± 2.9 mm the difference is not significant (P>0.5).In the distal end the mean height in males is 13.1 ± 2.1 mm while in females it is 12.5 ± 2.3 mm the difference is not significant as well (P>0.5).The difference in height between the proximal and distal ends in males is not significant (P>0.05),but still that means distal end is higher than the proximal by 2.4 mm.In females, the distal end is significantly higher than the proximal end by 2.6-mm (P<0.05).From the measurement of width and height, it is clearly shown that the profile of the proximal end are elliptical in shape while distal end profile is more or less circular in shape.
The mean C.S.A. of the proximal end in males is 151.2 ± 62.3 mm 2 , while in females it is 135.6 ± 60 mm 2 (table1 & 2), this demonstrate that the mean tunnel inlet CSA is smaller in females than males but the difference is not significant (P>0.5).In distal end, the CSA again is smaller in females and equal to 145.8 ± 49.3 mm 2 as shown in Table II, compared to male value of 160.4 ±46.8 mm 2 as shown in (Table 1), which show that males have larger CSA of the outlet but it is also not significant (P>0.5).In correlating these findings in both males and females the distal end is larger by 9.2 and 10.2 mm 2 respectively than proximal end, that makes the tunnel cone in shape with its base looking distally, the differences between the two ends are not significant (P >0.5) both in males and females.
The volume of the carpal tunnel (Table I and II) was calculated from the mean of the CSA of both proximal and distal ends multiplied by the length of the tunnel of the same specimen measured directly from the cadavers.The mean volume of the tunnel in males is 4.6 ± 2 cm 3 (Table I), while in females the volume is 3.7 ± 1.4 cm 3 (Table II).There is a difference of 0.9 cm 3 between sexes, which is not significant (P>0.5) that still leaves the males with larger carpal tunnel volume.
The age and sex relations to tunnel volume are shown in fig. 1and 2. The pattern in females is large volume at the age of 40 year, then the tunnel capacity decrease steadily till the age of about 70 year, the volume then starts to increase again.The age between 40-60 years is the age of maximum incidence of carpal tunnel syndrome.In males, the picture is different; the volume is steady till the 4 th decade then it starts to increase till late 50s followed by a decrease in size below the values of the 40s. Figure 3, show both females and males data blotted together, it show that during the active period of life males are less susceptible to carpal tunnel compression than females, this goes well with the clinical observation of higher incidence in females i.e. 80% of affected females are over 40 years 11 , that can be explained partially by small tunnel volume and partially by increase bulk of the contents during diseases or illnesses as rheumatoid arthritis, myxoedema or pregnancy, results in median nerve compression and ischaemia.

Discussion
In reviewing the literatures of the last three decades, it appears that the Vernia has been used for the first time in such study to measure the three dimensions of the carpal tunnel.
The length of the carpal tunnel was measure directly from the cadavers (Table I and II).Although there are differences in the means between sexes but they are not significant, which can be attributed to the differences in the hand size between men and women in general.Pierre 12 , using the MRI found that the mean length of the tunnel in women (in general) was 36.3 ± 3.4 which is 10.1 mm more than the female figures for the carpal tunnel length in this series, but if Pierre figures are corrected by the correction index for the tunnel (which is 0.8161) advocated by Cobb et al and Richman et al 13,14 , then the differences between this work and Pierre results will be slight (3mm).Kunou et al 15 also found that there is no significant difference between male and female in length of the carpal tunnel, which is a similar result as this work.
The width of the proximal and distal ends showed little differences between sexes (table 1 & 2), male have wider canal in proximal and distal end, which is 0.6 and 0.7 mm respectively, but it is not significant.There is a large significant difference between inlet and outlet in both males and females i.e. proximal end of the carpal tunnel is wider than the distal end, which is in agreement with the finding of Takechi and his group 16 , they found that the proximal end is wider than the distal end but they did not mention any age or sex differences they also found that the width in the inlet is 35 mm which is nearly double the overall figure of this series (17.75 mm mean of combined reading of males and females), the reason behind this large difference is that Takechi and coworkers used the carpal eminence's as a measuring point while in this series the measurements were done by the vernia directly from the inside of the carpal tunnel, there is as well an element of magnification in radiological films 17 , used by Takechi and his workers.All these account for the differences in the two figures.Not all workers accept no sex differences in the tunnel width, Kunou and co-worker 15 found that the width is different between male and female being narrow in females as our finding in this work.Females' carpal tunnel is narrower at both ends but not significant.
The height of the tunnel at the proximal end and at the distal end.In this work the height of the tunnel was measured carefully because it is of importance in calculating the CSA exactly and to have an idea about the shape of the proximal and distal ends cross section.Slight differences were found in the height between sexes with the males' tunnel slightly but not significantly higher than females at both ends (0.8 and 0.6 mm).The differences between height of the proximal and distal ends were found to be significant with the distal end is higher than the proximal.
As a result of having an elliptical shape inlet, the carpal contents as they pass through this elliptical proximal end will spread transversely making them less liable to compress on each other during wrist movement in flexion and extension as the proximal end is at the most mobile part of the wrist (carpo-radial joint).In distal end which is circular the contents are crowded in a circular manner which make them more liable for compression if the distal end is as freely mobile as the proximal end, but the line of movements of flexion and extension is not passing through the carpo-metacarpal joint i.e. distal carpal tunnel end 18 .
The CSA of the proximal and the distal ends of the carpal tunnel show some differences regarding the sex and age (Table I and II).At the proximal end the difference between males and females is not significant also at the distal end, the males have larger overall CSA but it is not significant, that still leaves the males with larger overall CSA of the carpal tunnel.
Regarding the differences in CSA between proximal and distal ends, in males the proximal end is smaller than distal end but it is not significant, the shape of the tunnel from these measurements is conical with it's base looking distally.In females the proximal end is smaller than the distal end also it's not significant, tunnel shape is conical as well with its base looking distally.Dekel et al 6 also found that females have smaller CSA than males in both proximal and distal ends, their measurements were done by the CT scan, their figures were larger as compared with this work which is partially due to the magnification in the CT scan.Another work was done by Bleecker 19 who examined CSA in 7 normal males again by the CT scan, he found that their CSA were 2.53 ± 0.15 cm 2 which is larger than this work value in males but there is also an element of magnification in the CT scan film 17,20 Pierre et al 12 found that the inlet is larger than the outlet, all their cases were normal females examined by MRI their finding is opposite to this work finding.Skie et al 21 measure the CSA at the hook of hammat level (distal end) and found similar CSA figures as this work during neutral position of the wrist (CSA = 1.52 cm 2 ) they also found that the CSA is more during extension and less during flexion.Ham et al 22 similarly measured the CSA at hook of hammat and found that the CSA with the fingers in flexion and extension positions are 191± 26 mm 2 and 169±15 mm 2 respectively which mean that the neutral position is some where in between i.e. 180 mm 2 which is larger than this work figures (MRI magnification).In both groups the findings of large CSA in extension of the wrist and flexion of fingers fits with the clinical observation of relief of symptom during wrist extension 23 The volume of the carpal tunnel was calculated as the mean of the volumes (table 1 & 2) a difference of 0.9 cm 3 between males and females but its not a significant one.Richmann et al 13 Measured the tunnel capacity directly by silicon mold and by MRI and found that the mold volume is 4.73± 1.01 ml while by MRI it is 5.84±1.24ml which is 4.77 ml when corrected 14 , the corrected figures are near to this work figures.
The relations between age, sex and volume of the carpal tunnel are studied (figures 1 and 2).In females, there is a change in tunnel capacity according to the age, large tunnel volume was noticed at the two extremes of age and small volume during the fourth to sixth decades which is the period recognized clinically as the period of high risk for carpal tunnel syndrome 8 .In males the shape of the curve is different, there is a steady curve at fourth decade then increase in volume capacity of the tunnel till late sixties followed by drop in size, this explain the low incidence of the syndrome in males during the active period of life.During this period females have small tunnel volume while males have large tunnel volume that explain the overall incidence of median nerve compression M: F =1: 4 Ferry et al 12 suggest some hormonal factors in females which may contribute to the high number of female cases, small tunnel will not cause the compression of the nerve alone this is true in non idiopathic cases as there should be a pathology precipitating the compression.In idiopathic cases, it is the decrease of the tunnel volume, which may lead to the symptoms.Manarguez 3 found that 84% of the cases of compression were bilateral which suggest inherited abnormalities.Pierre et al 12 agreed that the anatomy of the tunnel do change by age but they found that women over 45 have larger tunnel than younger women this is not our finding.Dekel et al 6 rejected the idea of any relation between age and size of the tunnel.It was also rejected by Winn et al 25 who stated that small carpal canal area does not appear to be a risk factor in carpal tunnel syndrome but from this work it is clear that the size and structure of the tunnel are changed according to age and sex which partially explained the high incidence of compression of the median nerve in females during the active period of life.

Conclusions (1)
The proximal end of the carpal tunnel is smaller than the distal end and its contents are more bulky, so the chance of getting compression of the nerve at proximal end is higher than the distal end and hence the importance of good decompression in proximal end.(2)  There is a difference in the measure-ments of carpal tunnel between males and females.(3)  CSA & volume of the carpal tunnel differs according to age and sex.(4)  Idiopathic causes of median nerve compression are merely a manifes-tation of volume changes in different age groups.(5)  The non-idiopathic type is due to increase in the volume of the contents within the tunnel by the presence of pathology, which overcome the available expansion space.

Fig 1 .
Fig 1. Volume of carpal tunnel in relation to age Fig 2. Volume of carpal tunnel in relation to age in male.infemale